Preparation of dialkylalkanamides



Patented July 15, 1952 NLIITE D s A E S BnErARAT-IoNoF DIALK LA KANAMIDEs. i Rudolph L; Heider, Dayton, Ohio, assignor' to Monsanto Chemical Company, St

corporation of Delaware Louis, Mo., 21.

'No Drawing. .,Application July 20, 1949, i

serial No. 105,889 1 l The present invention is concerned with a chemical process for the production of particular chemical compounds. v v I It is an object of the invention to produce "dialkyl acylamidesby a novel process-which avoids the difficulties inherent in processes of the prior art. It is a specific object of the invention to prepare dimethyl acetamide and higher dimethyl acylamides. Other objects 'of the invention will become apparent hereinafter.

The methods heretofore employed in the manufacture of dialkylamides have been characterized by difliculties in the separation of the desired compounds. For example, J. R. Ruhoff and E. Emmett Reid, in an article entitled -A Series of Aliphatic Dimethyl'Amides in the Journal of the American Chemical Society, '59, 401 (1937), describe the preparationof such compounds as azeotropic mixtures with acids. Such mixtures cannot be separated by ordinary distillation methods, so that the isolation of'the dialleylamides requires the use of expensive treating methods.

tIt'hasInow been found that the di'flicultiesflof the priorga-rt may-be overcome by the manufacture of alkyl-substituted acylamides by a process in which a tris(dialkylamido) phosphateis reacted with analiphatic acid. The process of the present invention avoids the formation of interfering azeotropes, so that substantially pure amides may be prepared.

The preparation of tris(.dialkylamido') phosphates :is described in .copending application, Serial No. 28,723, filed May.22,11948, and assigned to the same assignee as is the present application. The higher substituted 'homologues of such phosphates may also be employed in the process of the present invention. The preparation of a typicali-compound .is shown below.. The tris(dimethylamido) :phosphate was prepared by reacting phosphoryl chloride, .PQCla, and dimethylamine in a solvent such .astoluene. In carrying out this reaction, '153 g. of .phosphoryl chloride in 2-liters of toluene-were treated at about 50 with, dime'thylamine until saturation'was observed. The reaction mixture wasv then 1 heated to-lOQ? while bubbling in further .dimethylami'ne until saturation; "The solid material was "filtered on rand was 'then' heated to distill-off to'luenel 'Ihecrude product was washed with small' amounts' of concentrated sodium carbonate in toluene. The puretris"(di-' methylami'do') phosphate which was obtainedby distillation of the crude product "gave a yield of 116 g. as a clear, colorless liquid having a boiling 5 Claims; (01. 2605561) :acylamide.

pointof 7.6.a't 1 mm.pressure anda refraetive index, n 5::'1.-4570. Other solvents which are inert with respect tothe phosphoryl chloridemay also be used. Thus, benzene, ethyl benzene, xylenes or mixtures thereof may also be used.

An equation expressing the probable course of the chemical reaction of the process of the invention is shown below-as an illustrationpfa typical compound, namely, tris(dimethylamido) *Since-it is not possible atthistime to state the entire mechanism-of the reaction involved inthe process of this invention, "the invention is not invention. I a

Although the mechanism of the reactionisnot entirely elucidated, it would appearthat the limited by any theoriesas to'the process of' the aliphatic acid forms a complexQ-or is hydrogenbonded to the tris(dimethylamido) phosphate, so

that a'maximumboiling azeotrope having a rel'atively high boiling point is obtained; In the heating and distillation step" any "excess acid is' first removed, after which the hydrogen-bonded complex decomposes thermally to yield the di'alkyl Sincethere is no appreciable aliphatic acid present after this decomposition stage, theamide 'cannot form an azeotropewit'h an acid, so that the amide is obtained as a substantially pure product. The heating st'ep-does not require any critical temperature, 'butfor-convenience may be carried outrat the boiling tem'- :perature of the dialkyl .acylamide, either atfat mospheric pressure or undervacu'um; sothatthe product may be withdrawn by distillation: The following examples illustrate. the gen vention is-rs-concerned;without; 1h'lmzeve'r, limiting the; invention to the. precise methods disclosed:

mixed with "1-50-1111. of glacial acetic ac'icl in a reaction-vessel. --The mixture was 'heated' -"and a al process and type "of iireaction with which-Ethefin- 3 vacuum of about 100 mm. Hg was applied to the system which was maintained under refluxing conditions by means of a distillation column mounted on the reaction vessel. After about onehalf hour an overhead stream was withdrawn from the system at a still head temperature of 60 C. to62 C. The preliminary forerun of 104 ml. corresponded to unreacted acetic acidas indicated by the refractive index, n =l.3709.

The remainder of the distillation was carried out at a temperature of 96 C. at 80 mm. pressure and yielded 51.8 grams of dimethyl acetamide free from azeotropes. The refractive index ofthis product was n =1.4358.

The yield based upon the acetic acid was 73.5%

Easample 2 The use of formic acid was shown by a run in which one mole of tris(dimethylamido) phosphate was reacted with a 50% molar excess of formic acid. After equilibrium was reached in the distillation flaskv maintained under vacuum, the, unreacted formic acid was distilled off, and the'dimethyl formamide recovered as the primary product.

' Example 3 continuous method. In continuous operation a reaction vessel equipped with a distillation columnris continually'charged with tris(dimethylamido) phosphate and the acid corresponding to the desired alkyl substituted acylamide, The preferred; acids which I may employ arethe aliphatic 'acids having from one to five carbon atoms, although my process is i also applicable to higher acids. The reaction vessel is heated by suitable means and is preferably equipped with vacuum connections so that the process maybe carried out at lower temperatures to avoid side reactions and decomposition to high polymeric forms. of phosphate compositions. The process may, also employ 'acontinuous removal of bot- ;toms,such as the residual phosphorus compound.

-The continuous process jinwhich tris(dialkylamido) phosphate and the desiredaliphatic acids are continua ly charged employs; astill from which a-va'por stream. is removed. This stream consists ofunreactedacidwhich may be re-,

cycled to the process.

.7 The bottoms-from the-first still-or reactor are then charged into a second still, from which an overheadlproduct consisting of the N,N-dialkyl acylamide'may be withdrawn. This second still is also equipped with a bottom draw-off for higher boiling materials;

The-reaction may advantageously'be carried out under reduced'pressure in order to operate at a lower temperature and thereby prevent decomposition. However, the reaction may also be car ried out at atmospheric pressure, or at elevated pressures, if desired. The distillation step which is employed to separate the reaction product may be carried on duringthecontinuous reaction of theabove components in the reaction vessel, or

which is followed by a pure cut of dimethyl acet- V amide.

Itis an advantage of the present process that no azeotrope is formed with the N,N'-dialkyl acylamide, so that the product is obtained free fromwater or acid. In contrast to this process, the method of Ruhoff and Reid, described above, which has been applied to the production of simple substituted amides, has the disadvantage that maximum boiling azeotropic mixtures of the N,N-dialky1 acylamide and the corresponding aliphatic acid are obtained in the isolation of the final product. Such maximum azeotropic or constant-boiling mixtures cannot be separated by direct distillation, so that other methods must be employed at greater cost to obtain a pure product. V In general it is not critical to employ any par.- ticular proportions of the amidophosphate and the aliphatic. acid, although it is preferable to employ an excess of the acid, so that the most efiective utilization of the amidophosphate may be practised by hydrogen-bonding all of this constituent. The amidophosphate compound is preferably tris(dimethylamido) phosphate, and the acid is preferably in the group of 1 to 5 carbon atom aliphatic acids or a lkanoic acids.

The .reaction conditions are not criticaland may be carried out at atmospheric pressure, or under vacuum 9 Super-atmospheric conditions. However, it is preferable to employ a; vacuum, so that the finishedproducts, and unreacted' components may be distilled overhead with a minimum of side reactions. 1

The reaction temperature is not' critical since the preliminary bonding of the acid and the amidophosphate occurs very readily, although this. loose combination is broken in the heating step in which the desired dialkyl acylamide is vaporized while heating. Such heating may'preferably be done at the conditions corresponding to the boiling point of the' dialkyl .acylamide.

1 While I have described certain preferred forms of the invention, it is'under'stood that this is by way of illustration only, and various changes may be'made within the scope of the appended claims without departing from the spirit ofthe invention which is not to be limited to the specific embodiments herein-described or' specifically covered by the claims.

What is claimed and is desired to be protected by Letters Patent of the United Statesis:

1'. The process for preparing lower dialkyl acylamides, which comprises heating a mixture of a tris(dialkylamido) phosphate in which the alkyl groups have from 1 to 2 carbon atoms, withan alkanoic acid having from 1 to 5 carbon atoms, said alkanoic acid being in s'toichiometric excess over the said tris(dialkylamido) phosphate, said reaction occurring at a temperature approximately that of the boiling point of the said dialkyl acylamides.

2. The process-for preparing." dimethyl acylamides, which'comprises heating a' mixture of tris(dimethylamido) phosphate with an alkan'oic acid having from ;1 to 5=carbon atoms, said alkanoic acid being in stoichiometricexcess over the said 'tris(dimethylamido).;;.jphosphate,-, Said-r8810,-

tionoccurring at a'temperature approximately that. of the boiling point :of the said dimethyl acylamides. v i

3. The process for preparing dimethyl formamide, which comprises heating a mixture of tris(dimethy1am.ido) phosphate with formic acid, said formic acid being in stoichiometric excess over the said tris(dimethylamido) phosphate, said reaction occurring at a temperature approximately that of the boiling point of the said'dimethyl formamide.

4. The process for preparing dimethyl acetamide, which comprises heating a mixture of tris(dimethy1amido) phosphate with acetic acid, said acetic acid being in stoichiometric excess over the said tris dimethy1amido phosphate, said reaction occurring at a temperature approximately that of the boiling point of the said dimethyl acetamide.

5. The process for preparing dimethyl propionamide, which comprises heating a mixture of tris(dimethylamido) phosphate with propionic acid, said propionic acid being in stoichiometric excess over the said tris(dimethy1amido) phosphate, said reaction occurring at a temperature approximately that of the boiling point oi. the said dimethyl propionamde.

RUDOLPH L. HEIDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,160,841 Dreyfus June 6. 1939 2,408,633 Guenther et a1. Oct. 1, 1946 FOREIGN PATENTS Number Country Date 610,952 Great Britain Oct. 22, 1946 

1. THE PROCESS FOR PREPARING LOWER DIALKYL ACYLAMIDES, WHICH COMPRISES HEATING A MIXTURE OF A TRIS (DIALKYLAMIDO) PHOSPATE IN WHICH THE ALKYL GROUPS HAVE FROM 1 TO 2 CARBON ATOMS, WITH AN ALKANOIC ACID HAVING FROM 1 TO 5 CARBON ATOMS, SAID ALKANOIC ACID BEING IN STOICHIOMETRIC EXCESS OVER THE SAID TRIS(DIALKLAMIDO) PHOSPHATE, SAID REATTION OCCURRING AT A TEMPERATURE APPROXIMATELY THAT OF THE BOILING POINT OF THE SAID DIALKYL ACYLAMIDES. 